hesitate vs plug away

hesitate

verb
  • To stop or pause respecting decision or action; to be in suspense or uncertainty as to a determination. 

  • To stammer; to falter in speaking. 

  • To utter with hesitation or to intimate by a reluctant manner. 

plug away

verb
  • To persist or continue, as with an effort. 

How often have the words hesitate and plug away occurred in a corpus of books? (source: Google Ngram Viewer )